An end-of-line (EOL) monitor and test system was developed to verify the operation of a sound system in facilities such as airports, convention centers, industrial and stadiums. The system operates by sending an inaudible tone over the normal sound system, typically in the range of 19 KHz to 20 KHz, and then measuring the voltage and current of the power amps driving the speakers. A fault is declared for any change in the impedance of the load which causes a voltage or current deviation, compared to a preset level, greater than a pre-determined fault threshold.
The EOL monitor and test system will identify a fault on a single line, but does not tell where on the line the fault occurred. The EOL monitor and test system also will not tell if a line is cut to a speaker on a branch, or, if there are a lot of speakers on the circuit, it will not tell if there is a fault on a single speaker because the change will be too small to measure. To overcome this, all the speakers can be wired in serial fashion on one wire and putting some kind of detecting device on the end of that line, such as an EOL device. This is a very expensive way to wire speakers, and most existing installations run a line down a single hall or corridor and branch off to the sides to areas with one or more speakers in them. If one of these branches is broken, it could not be detected using the EOL device.
Accordingly, the end-of-branch (EOB) system of the present invention was developed to overcome these problems. Accordingly, it is desirable to be able to detect faults in individual speakers on audio signal lines that are branched from a trunk audio signal line. In addition, it is desirable to achieve such fault detection with a minimum of expense. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
The ability to individually address each speaker leads to another use of the EOB with the addition of a new switch (T) that is connected to another set of terminals so an individual speaker (V) can be disconnected by command. This would allow routing audio to any or all speakers on the amplifiers output from the main system. This would allow paging to a single room without disturbing the whole building, and in turn, turning off a conference room that does not warrant to be interrupted. This could be used with or without the end of line testing that is the primary use of the EOB module.